Naval fire-control radar

The development of precision radar for the control of naval guns is described from its introduction in 1940 as a simple range-finder of medium precision to the complicated automatic systems which make accurate fire-control possible under all conditions of visibility. The introduction of radar revolutionized naval gunnery, because intermittent and inaccurate ranges obtainable with the optical rangefinder were replaced by continuous ranging of comparatively high accuracy. Narrow beams are shown to be necessary for fire-control radar sets in order to avoid confusion when several targets are in the vicinity of a ship at the same time. It follows that, since space and weight limitations necessitate small aerial systems, the highest possible frequency must be used. The successive development of equipments in the 600-, 3 000- and 10 000-Mc/s bands is described. The methods of tracking a target in polar co-ordinates are described in some detail, since the effect of fading of the signal reflected from the target is of particular importance in this case. It is shown that though the ?present position? of the target can quite easily be followed with an accuracy of a few minutes of arc, fading introduces rapid fluctuations which cause large errors in the measured angular rates. This necessitates smoothing over a period of several seconds, which introduces systematic errors into the computed course and speed of the target. A method (devised in the Admiralty Gunnery Establishment) of reducing the effect of this systematic error on the predicted future position is described. The paper ends with an account of radar methods for locating the shell-splashes relative to the target so that corrections can be made to the calculated future position.